The proposed research is principally aimed at the discovery and development of novel synaptic receptor toxins as probes to augment the understanding of synaptic transmitter mechanisms in the nervous system. The focus is on synaptic transmission mediated by amino acids and peptides. Spiders have evolved highly potent venom toxins to immobilize their insect prey. Paralysis results from a "curare-like" blockade of skeletal neuromuscular transmission which, for insects, involves amino acid transmitters. The applicant seeks to investigate the physiological basis for synaptic block caused by novel toxins recently isolated form Orb Weaver and Funnel Web spider venoms. The toxins appear to function as specific receptor antagonists affecting L-glutamate and L-aspartate transmission at nerve-muscle junctions. They are low molecular weight substances which exhibit novel structural features suggestive of a pseudo-peptidic character. Estimated potencies of the toxins are in the micromolar to nanomolar range, making them among the most active amino acid antagonists thus far described. Electrophysiological techniques are to be used for the analysis of toxins activity on model synaptic preparations mediated by glutamate, aspartate and the pentapeptide, proctolin. The applicant further proposes to conduct a systematic study of spider venoms designed to uncover new toxins affecting amino acid and peptide synaptic transmission. This will be accomplished by combining methods for HPLC purification and bioassay of toxins on in vivo and in vitro synaptic preparations. Excitatory amino acids are considered a major class of brain neurotransmitters. Amino acid receptor antagonists have already shown promise as a potential class of new central anticonvulsants which could ultimately lead to improved therapeutic approaches to seizure syndromes in the brain. The spider toxins may be the most potent and specific amino acid receptor antagonists yet discovered. As such, they hold promise for the creation of effective pharmacological and biochemical probes useful in developing studies and therapies involving amino acid transmitter mechanisms.